Nefopam (brand names: Acupan, Silentan, Nefadol and Ajan) is a centrally-acting but non-opioid analgesic drug of the benzoxazocine chemical class which was developed by Riker Laboratories in the 1960s. It is widely used, mainly in European countries, for the relief of moderate to severe pain as an alternative to opioid analgesic drugs. Animal studies have shown that nefopam has a potentiating (analgesic-sparing) effect on morphine and other opioids by broadening the antinociceptive action of the opioid and possibly other mechanisms, generally lowering the dose requirements of both when they are used concomitantly.
§Use
Nefopam has additional action in the prevention of shivering, which may be a side effect of other drugs used in surgery. Nefopam was significantly more effective than aspirin as an analgesic in one clinical trial, although with a greater incidence of side effects such as sweating, dizziness and nausea, especially at higher doses. Nefopam is around a third to half the potency and slightly less effective as an analgesic compared to morphine, or oxycodone, but tends to produce fewer side effects, does not produce respiratory depression, and has much less abuse potential, and so is useful either as an alternative to opioids, or as an adjunctive treatment for use alongside opioid(s) or other analgesics. Nefopam is also used to combat severe hiccups.
§Side effects
Common side effects include nausea, nervousness, dry mouth, light-headedness and urinary retention. Less common side effects include vomiting, blurred vision, drowsiness, sweating, insomnia, headache, confusion, hallucinations, tachycardia, aggravation of angina and rarely a temporary and benign pink discolouration of the skin or erythema multiforme.
§Contraindications
It is contraindicated in people with convulsive disorders, those that have received treatment with irreversible monoamine oxidase inhibitors such as phenelzine, tranylcypromine or isocarboxazid within the past 30 days and those with myocardial infarction pain, mostly due to a lack of safety data in these conditions.
§Interactions
It has additive anticholinergic and sympathomimetic effects with other agents with these properties. Its use should be avoided in people receiving some types of antidepressants (tricyclic antidepressants or monoamine oxidase inhibitors) as there is the potential for serotonin syndrome or hypertensive crises to result.
§Recreational use and overdose
Recreational use of nefopam and death from overdose have both been reported, although these events are less common with nefopam than with opioid analgesic drugs. Overdose usually manifests with convulsions, hallucinations, tachycardia and hyperdynamic circulation. Treatment is usually supportive, managing cardiovascular complications with beta-blockers and limiting absorption with activated charcoal.
§Pharmacology
The mechanism of action of nefopam is not well understood, although inhibition of serotonin, dopamine and noradrenaline reuptake is thought to be involved in its analgesic effects, and there may be other modes of action such as through histamine H3 receptors and glutamate. Recently, like its analogue orphenadrine which also has analgesic effects, nefopam has been found to act as a voltage-gated sodium channel blocker, and this may in part or fully mediate its antinociceptive effects.
§See also
- Orphenadrine